JP7174332B2 - All-solid battery - Google Patents

Description

The present invention relates to all-solid-state batteries.

In recent years, secondary batteries such as lithium secondary batteries have been used in portable power sources such as personal computers and mobile terminals, and power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is preferably used.

With the spread of secondary batteries, further improvement in performance is desired. As a high-performance secondary battery, an all-solid-state battery in which the electrolytic solution is replaced with a solid electrolyte has attracted attention. An all-solid-state battery typically includes a laminate in which a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode are laminated (see, for example, Patent Document 1). The laminate is housed in a battery case such as a laminate case. In Patent Document 1, from the viewpoint of improving cycle characteristics, an oxide layer having an oxygen concentration of 20 atomic % or more and a thickness of 35 nm or less is provided on the outer peripheral portion of a sulfide solid electrolyte.

JP 2012-160379 A

It is known that a sulfide solid electrolyte reacts with moisture in the air to generate gas (H ₂ S). Therefore, when the laminate film of the case of the all-solid-state battery is opened and the sulfide solid electrolyte comes into contact with air, there is a problem that gas is generated. In order to suppress the generation of this gas, it is conceivable to include reaction inhibitors in the all-solid-state battery, but the inclusion of reaction inhibitors that do not contribute to the battery reaction leads to a decrease in the energy density of the all-solid-state battery. I don't like it.
In Patent Document 1, an oxide layer is provided on the outer periphery of the sulfide solid electrolyte. Therefore, a gas containing 100 ppm of water is sprayed, and this gas flow rate may lead to deliquescence of the sulfide solid electrolyte. It is considered that when this deliquescence occurs, it may become impossible to suppress the generation of gas. Moreover, since the positive electrode and the negative electrode also contain a solid electrolyte, it is necessary to suppress the reaction between the sulfide solid electrolyte and water in the positive electrode and the negative electrode. Therefore, the technique described in Patent Document 1 has a problem in suppressing gas generation due to reaction between the sulfide solid electrolyte and moisture in the air when the laminate film is opened.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an all-solid-state battery in which generation of gas due to reaction between a sulfide solid electrolyte and moisture in the air is suppressed when air enters the battery.

The all-solid-state battery disclosed herein includes a laminate having a positive electrode, a negative electrode, and a sulfide solid electrolyte layer interposed between the positive electrode and the negative electrode, and a laminate case accommodating the laminate. The positive electrode contains a positive electrode active material and a sulfide solid electrolyte. The negative electrode contains a negative electrode active material and a sulfide solid electrolyte. The sulfide solid electrolyte of the positive electrode, the sulfide solid electrolyte of the negative electrode, and the sulfide solid electrolyte of the sulfide solid electrolyte layer each contain LiI. A passivation layer is provided on the end face of the laminate. The passivation layer contains LiI hydrate.
According to such a configuration, an all-solid-state battery is provided in which generation of gas due to reaction between the sulfide solid electrolyte and moisture in the air when air enters the interior is suppressed.

1 is a cross-sectional view schematically showing the configuration of an all-solid-state battery according to one embodiment of the present invention; FIG. 1 is a cross-sectional view schematically showing the configuration of a laminate included in an all-solid-state battery according to one embodiment of the present invention; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments according to the present invention will be described with reference to the drawings. Matters other than those specifically mentioned in this specification that are necessary for the implementation of the present invention (for example, the general configuration and manufacturing process of an all-solid-state battery that does not characterize the present invention) It can be grasped as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Further, in the following drawings, members and portions having the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

FIG. 1 schematically shows the configuration of an all-solid-state battery according to this embodiment. FIG. 2 schematically shows the configuration of the laminate provided in the all-solid-state battery according to this embodiment.
The all-solid-state battery 10 includes a laminate 20 and a laminate case 60 that accommodates the laminate 20, as shown in FIG. The laminate 20 has a positive electrode 30, a negative electrode 40, and a sulfide solid electrolyte layer 50 interposed between the positive electrode 30 and the negative electrode 40, as shown in FIG.

In this embodiment, a sulfide solid electrolyte is used as the solid electrolyte. Therefore, the sulfide solid electrolyte layer 50 contains a sulfide solid electrolyte. Sulfide solid electrolytes have high ionic conductivity.
In this embodiment, one containing LiI is used as the sulfide solid electrolyte. As the sulfide solid electrolyte containing LiI, a known one used in all-solid-state batteries may be used, and a Li _{2 S-based solid solution composed of Li 2 S} and lithium iodide (LiI) is preferably used. be done. Examples of such sulfide solid electrolytes include LiI—Li ₂ SP ₂ S ₅ , LiCl—LiI—Li ₂ SP ₂ S ₅ , LiBr—LiI—Li ₂ SP ₂ S ₅ , LiI -Li ₂ S-SiS ₂ , LiI-Li ₂ S-B ₂ S ₃ and the like.
The average particle size of the sulfide solid electrolyte is, for example, about 0.5 μm to 10 μm, preferably about 1 μm to 5 μm.
In this specification, unless otherwise specified, the "average particle size" corresponds to a cumulative 50% from the fine particle side in the volume-based particle size distribution measured by particle size distribution measurement based on the laser diffraction/light scattering method. It refers to the particle size ( _D50 particle size, also called median size).

The sulfide solid electrolyte layer 50 may further contain a binder or the like.
As the binder, fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), and rubber-based binders such as styrene-butadiene rubber (SBR) can be preferably used.

The positive electrode 30 has a positive electrode current collector 32 and a positive electrode active material layer 34 provided on the positive electrode current collector 32, as shown in FIG. In the illustrated example, the positive electrode active material layer 34 is provided on both sides of the positive electrode current collector 32, but the positive electrode active material layer 34 is provided on one side of the positive electrode current collector 32. good too.

As the positive electrode current collector 32, any material that can be used as a positive electrode current collector for an all-solid-state battery can be used without particular limitation. Typically, the positive electrode current collector 32 is made of a metal having good conductivity, such as aluminum, nickel, titanium, stainless steel, or the like. Aluminum is particularly preferred. The positive electrode current collector 32 is preferably a foil-like body as shown in the drawing. Therefore, aluminum foil is preferable as the positive electrode current collector. Although the thickness of the positive electrode current collector 32 is not particularly limited, it is preferably about 5 μm to 50 μm, more preferably about 8 μm to 30 μm, in consideration of the balance between the capacity density of the battery and the strength of the current collector.

The positive electrode active material layer 34 contains a positive electrode active material and a sulfide solid electrolyte. Although the thickness of the positive electrode active material layer 34 is not particularly limited, it is, for example, about 10 μm to 500 μm.
A positive electrode active material is a material capable of reversibly intercalating and deintercalating charge carriers (eg, lithium ions). A known compound used as a positive electrode active material in an all-solid-state battery may be used as the positive electrode active material. Suitable examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiNi _x Co _y Mn _(1-xy) O ₂ (where 0<x<1, 0<y<1, 0<x+y<1), etc. and a lithium composite oxide having a layered structure. Alternatively, Li ₂ NiMn ₃ O ₈ , LiMn ₂ O ₄ , Li _1+x Mn _{2- y} My O ₄ (where M is absent or one or more selected from Al, Mg, Co, Fe, Ni and Zn and spinel-structured lithium composite oxides represented by 0≤x<1, 0≤y<2), olivine-structured lithium composite compounds such as _LiFePO4 , and the like.
The average particle size of the positive electrode active material is, for example, about 0.5 μm to 20 μm, preferably about 1 μm to 10 μm.

The sulfide solid electrolyte contained in the positive electrode active material layer 34 contains LiI. Examples of such a sulfide solid electrolyte include those used for the sulfide solid electrolyte layer 50 . The sulfide solid electrolyte contained in the positive electrode active material layer 34 may be the same as or different from the sulfide solid electrolyte of the sulfide solid electrolyte layer 50, and is preferably the same.
The compounding ratio of the positive electrode active material and the sulfide solid electrolyte in the positive electrode active material layer 34 is not particularly limited. Typically, the mass ratio (P:S) of the positive electrode active material (P) and the sulfide solid electrolyte (S) is about 50:50 to 95:5.

In addition to the positive electrode active material and the sulfide solid electrolyte, the positive electrode active material layer 34 may optionally contain various optional components. Examples of such optional components include conductive materials, binders, and the like.
Carbon black such as acetylene black and other carbon materials (graphite, carbon nanotubes, etc.) can be suitably used as the conductive material.
As the binder, fluorine-based binders such as PVDF and PTFE, and rubber-based binders such as SBR can be preferably used.

The negative electrode 40 has a negative electrode current collector 42 and a negative electrode active material layer 44 provided on the negative electrode current collector 42, as shown in FIG. In the illustrated example, the negative electrode active material layer 44 is provided on both sides of the negative electrode current collector 42 , but the negative electrode active material layer 44 is provided on one side of the negative electrode current collector 42 . good too.

As the negative electrode current collector 42, any material that can be used as a negative electrode current collector for an all-solid-state battery can be used without particular limitation. Typically, the negative electrode current collector 42 is made of a metal that is difficult to form an alloy with Li and has good conductivity, such as copper, a copper alloy, nickel, or the like. Copper is particularly preferred. The negative electrode current collector 42 is preferably a foil-like body as shown in the drawing. Therefore, copper foil is preferable as the negative electrode current collector. Although the thickness of the negative electrode current collector 42 is not particularly limited, it is preferably about 5 μm to 50 μm, more preferably about 8 μm to 40 μm, in consideration of the balance between the capacity density of the battery and the strength of the current collector.

The negative electrode active material layer 44 contains a negative electrode active material and a sulfide solid electrolyte. Although the thickness of the negative electrode active material layer 44 is not particularly limited, it is, for example, about 10 μm to 500 μm.

A negative electrode active material is a material capable of reversibly intercalating and deintercalating charge carriers (eg, lithium ions). A known compound used as a negative electrode active material in an all-solid-state battery may be used as the negative electrode active material. As the negative electrode active material, a carbon-based negative electrode active material, a silicon (Si)-based negative electrode active material, a tin (Sn)-based negative electrode active material, or the like can be used.
Examples of the carbon-based negative electrode active material include graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), and carbon nanotubes.
Examples of Si-based negative electrode active materials include Si, silicon oxide represented by SiO _a (where 0.05<a<1.95), silicon carbide represented by SiC _b (0<b<1), Examples include silicon nitride represented by SiN _c (0<c<4/3). Also, an alloy composed of Si and an element other than Si can be used. Examples of elements other than elemental Si include Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti.
Examples of Sn-based negative electrode active materials include tin, tin oxides, tin nitrides, tin-containing alloys, and solid solutions thereof. In addition, part of the tin atoms contained in these may be substituted with one or more elements. Tin oxides include tin oxide represented by SnO _d (0<d<2), tin dioxide (SnO ₂ ), and the like. Tin-containing alloys include Ni--Sn alloys, Mg--Sn alloys, Fe--Sn alloys, Cu--Sn alloys, Ti--Sn alloys, and the like. _SnSiO3 , _Ni2Sn4 , _Mg2Sn etc. _are illustrated besides this.
The average particle size of the negative electrode active material is, for example, about 1 μm to 20 μm, preferably about 2 μm to 10 μm.

The sulfide solid electrolyte contained in the negative electrode active material layer 44 contains LiI. Examples of such a sulfide solid electrolyte include those used for the sulfide solid electrolyte layer 50 . The sulfide solid electrolyte contained in the negative electrode active material layer 44 may be the same as or different from the sulfide solid electrolyte of the sulfide solid electrolyte layer 50, and is preferably the same.
The compounding ratio of the negative electrode active material and the sulfide solid electrolyte in the negative electrode active material layer 44 is not particularly limited. Typically, the mass ratio (N:S) of the negative electrode active material (N) and the sulfide solid electrolyte (S) can be about 50:50 to 95:5.

In addition to the positive electrode active material and the sulfide solid electrolyte, the positive electrode active material layer 34 may optionally contain various optional components. Examples of such optional components include conductive materials, binders, and the like.
Carbon black such as acetylene black and carbon materials such as vapor-grown carbon fiber can be suitably used as the conductive material.
As the binder, fluorine-based binders such as PVDF and PTFE, and rubber-based binders such as SBR can be preferably used.

The laminate 20 is housed in a laminate case 60 as shown in FIG. The laminate case 60 is made of a laminate film. As the laminate film, a known one used for laminate cases of all-solid-state batteries may be used. A laminate film typically has a structure in which a resin layer is provided on a metal foil. The metal foil is made of, for example, aluminum, an aluminum alloy, or the like. The resin layer is made of, for example, polyolefin such as polyethylene or polypropylene, polyester, nylon, or the like.

The all-solid-state battery 10 also has terminals (not shown) that are electrically connected to the laminate 20 in the laminate case 60 and protrude outside the laminate case 60 .

As shown in FIG. 2, the laminated body 20 is formed by alternately laminating positive electrodes 30 and negative electrodes 40 with sulfide solid electrolyte layers 50 interposed therebetween. An arrow Y shown in FIG. 2 indicates the stacking direction of the stack 20 .
In this embodiment, as shown in FIGS. 1 and 2, a passivation layer 22 is provided on the end surface of the laminated body 20 . The end face of the laminate 20 is a surface formed by peripheral edges of the positive electrode 30 , the negative electrode 40 , and the sulfide solid electrolyte layer 50 , and parallel to the stacking direction Y of the laminate 20 . Therefore, although the laminate 20 has four end faces, it is sufficient that the passivation layer 22 is formed on at least one end face, and preferably the passivation layer 22 is formed on all four end faces.
Passive layer 22 contains LiI hydrate (lithium iodide hydrate). LiI hydrates are, for example, LiI.H ₂ O and LiI.3H ₂ O.
In this way, the passivation layer 22 is provided on the end surface of the laminate 20, and the passivation layer 22 is hydrated with LiI, so that when air enters the laminate case 50, the sulfide solid electrolyte , the reaction with moisture in the air can be suppressed, and gas generation can be suppressed. In particular, not only the sulfide solid electrolyte layer 50 but also the positive electrode 30 and the negative electrode 40 can suppress gas generation due to reaction with moisture in the air.
Note that the fact that the passivation layer 22 contains LiI hydrate is determined by subjecting the passivation layer 22 to X-ray diffraction measurement. It can be confirmed by existence.

Passive layer 22 containing LiI hydrate is derived from LiI contained in the sulfide solid electrolytes of positive electrode 30 , negative electrode 40 and sulfide solid electrolyte layer 50 .
Therefore, in the example shown in FIG. 2 , the passivation layer 22 is not formed on the positive electrode current collector 32 and the negative electrode current collector 42 . Therefore, the passivation layer 22 is formed as a discontinuous layer on the end faces of the laminate 20 . However, the passivation layer 22 may be formed as a continuous layer on the end faces of the laminate 20 .

The passivation layer 22 containing LiI hydrate can be formed, for example, by placing the laminate 20 in a closed container such as a dry desiccator with a dew point of −30° C. or lower for 4 hours or longer.

All-solid-state battery 10 may be constrained. At this time, it may be in the form of a battery pack in which a plurality of all-solid-state batteries are bound while being electrically connected.

According to the all-solid-state battery 10 according to the present embodiment, generation of gas due to reaction between the sulfide solid electrolyte and moisture in the air when air enters the interior is suppressed. In particular, not only the sulfide solid electrolyte layer 50 but also the positive electrode 30 and the negative electrode 40 are inhibited from generating gas due to reaction with moisture in the air.
The all-solid-state battery 10 can be suitably used in applications where a secondary battery is used, and is particularly mounted on vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It can be suitably used as a driving power supply for

EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Example 1>
Micronized 80(75Li ₂ S-25P ₂ S ₅ )-20LiI (crystal) was prepared as a sulfide solid electrolyte.
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having a layered structure, the sulfide solid electrolyte, acetylene black as a conductive material, and PVdF as a binder were mixed in an inert gas at a ratio of 60:40. : mixed with heptane in a volume ratio of 5:2 to make a positive electrode slurry. This positive electrode slurry was applied to one side of an aluminum foil having a thickness of 15 μm and dried to prepare a positive electrode.
Further, in an inert gas, graphite, the sulfide solid electrolyte, acetylene black as a conductive material, and PVdF as a binder are mixed with heptane at a volume ratio of 50:45:5:2, A negative electrode slurry was prepared. This negative electrode slurry was applied to both sides of a copper foil having a thickness of 35 μm and dried to prepare a negative electrode.
Further, in an inert gas, the sulfide solid electrolyte and PVdF as a binder were mixed with heptane at a volume ratio of 100:2 to prepare an electrolyte layer slurry. This electrolyte layer slurry was applied to one side of an aluminum foil and dried to produce a transfer member having a sulfide solid electrolyte layer.

In an inert gas, the positive electrode, negative electrode and transfer member were cut according to the battery size. Two transfer members were respectively placed on the negative electrode active material layers formed on both sides of the negative electrode current collector, and pressed at a pressure of 4 ton/cm ² using a hot press. After that, the Al foil of the transfer member was peeled off, and the sulfide solid electrolyte layer was transferred onto the negative electrode active material layer. Next, the two positive electrodes obtained above were placed on the sulfide solid electrolyte layers transferred to both sides of the negative electrode, respectively, and pressed at a pressure of 4 ton/cm ² using a hot press. Thus, a positive electrode active material layer and a positive electrode current collector were formed on the sulfide solid electrolyte layer.
A two-layered cell was thus obtained. A laminate was produced by laminating 30 of the obtained two-laminate cells while adhering the positive electrode current collectors to each other with a binder.

The resulting laminate was stored in a dry desiccator with a dew point of −30° C. for 4 hours to form a passivation layer on the end surface of the laminate.
Thereafter, the laminate was placed in a glove box filled with an inert gas and housed in a laminate case to obtain an all-solid-state battery for evaluation.

<Comparative Example 1>
A laminate was produced in the same manner as in Example 1 and housed in a laminate case without being stored in a dry desiccator (that is, without forming a passivation layer) to obtain an all-solid-state battery for evaluation.

<X-ray diffraction measurement>
Using an X-ray diffractometer "RINT-Ultima III" (manufactured by Rigaku Co., Ltd.), the end face of the laminate in the stage before being housed in the laminate case of Example 1 and Comparative Example 1 was irradiated with Cu-Kα rays. X-ray diffraction measurement was performed in a scanning range of a diffraction angle 2θ=20 to 60° using a radiation source. The obtained X-ray diffraction patterns were examined for the presence or absence of crystal peaks characteristic of LiI hydrates (LiI.H ₂ O and LiI.3H ₂ O). Table 1 shows the results.

<Gas generation amount measurement>
A crucible filled with water and an _H2S sensor were placed in a cylindrical chamber. The evaluation all-solid-state battery was placed in a cylindrical chamber, the laminate case of the battery was opened, and the lid of the cylindrical chamber was closed to seal it. The amount of H ₂ S generated (ppm) was measured 10 seconds after the sealing. The ratio of the H ₂ S generation amount of the evaluation all-solid-state battery of Example 1 to the H ₂ S generation amount of the evaluation all-solid-state battery of Comparative Example 1 being 100 was obtained. Table 1 shows the results.

From the results in Table 1, it can be seen that in the evaluation all-solid-state battery of Example 1, a passivation layer containing LiI hydrate was formed on the end face of the laminate. It can be seen that the presence of this passivation layer significantly reduces the amount of gas generated.
Therefore, according to the all-solid-state battery according to the present embodiment, gas generation due to reaction between the sulfide solid electrolyte and moisture in the air can be suppressed when air enters the interior.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

10 All-solid-state battery 20 Laminate 22 Passive layer 30 Positive electrode 32 Positive electrode current collector 34 Positive electrode active material layer 40 Negative electrode 42 Negative electrode current collector 44 Negative electrode active material layer 50 Sulfide solid electrolyte layer 60 Laminated case

Claims (1)

An all-solid-state battery comprising a laminate having a positive electrode, a negative electrode, and a sulfide solid electrolyte layer interposed between the positive electrode and the negative electrode, and a laminate case housing the laminate,
The positive electrode contains a positive electrode active material and a sulfide solid electrolyte,
The negative electrode contains a negative electrode active material and a sulfide solid electrolyte,
The sulfide solid electrolyte of the positive electrode, the sulfide solid electrolyte of the negative electrode, and the sulfide solid electrolyte of the sulfide solid electrolyte layer each contain LiI,
A passivation layer is provided on the end surface of the laminate,
The end face of the laminate is a surface parallel to the lamination direction of the laminate,
wherein the passivation layer contains LiI hydrate;
An all-solid-state battery characterized by:

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